1. Field of the Invention
The present invention relates to a heave duty hinge for an aircraft service pit lid assembly that is used to provide access to subsurface pits located beneath airport runways, docking areas, and other surfaces across which aircraft travel.
2. Description of the Prior Art
At airports and airfields throughout the world, aircraft ground support electricity, air conditioning, fuel, and other aircraft servicing necessities are provided from pits located beneath the surfaces across which the aircraft travel. These pits provide subsurface terminations for aircraft servicing facilities such as fuel lines, electrical power supply lines, air conditioning ducts, and other auxiliary services which are provided to aircraft that are on the ground. The use of subsurface pits serves to reduce the congestion of motorized vehicles and lines running across the aircraft servicing areas that would otherwise exist.
Aircraft servicing pits typically take the form of hollow, fiberglass enclosures that are buried in excavated holes dug beneath aircraft servicing areas. Fuel lines, electrical lines, air conditioning lines and other ground support auxiliary service lines are typically laid down during the construction of the airport or aircraft terminal in trenches that are ultimately filled in. These lines run from the terminal facility to the aircraft servicing pits and are accessible through aircraft servicing pit lid assemblies that are located at the upper entrances to the pits. The pit lid assemblies employ surrounding frames in which pit lids are mounted by hinges for upward rotation about horizontal axes of rotation.
In some conventional subsurface aircraft service pit lid assembly arrangements the hinges are located atop the frame and protrude upwardly above a flat deck forming the upper surface of the frame. While quite convenient and easy to construct, upwardly projecting hinge assemblies have significant disadvantages. The are highly susceptible to damage by snow plows and ground support vehicles traveling over the pit lit assemblies. Consequently, it is currently more common for pit lid hinge mechanisms to be located within the pit and below the flat, upper surface of the deck surrounding the pit opening.
While locating the pit lid hinge assembly within the pit itself avoids the problems associated with exposed pit lid hinge assemblies, conventional hinge arrangements of this type present other problems. Conventional pit lid hinge assemblies that are located within the confines of a pit are expensive and relatively complex in construction. They typically involve spring mechanisms and multiple lever arms that can become fouled or broken over time. Furthermore, the use of conventional subsurface hinge assemblies located within the confines of the pit itself presents an obstruction to access to the lines terminating within the pit. A portion of the access opening is necessarily blocked by such a hinge mechanism, thus making it more difficult for ground servicing personnel to enter or reach down into the pit. Also, these obstructions can cause injury to ground servicing personnel as then enter or leave the pit through the access opening.
The present invention involves a subsurface hinge assembly for an aircraft servicing pit that avoid the problems associated with both hinge assemblies the protrude from the upper surface of the lid frame and also hinge assemblies located within the pit itself. The hinge assembly for a pit lid according to the present invention provides a hinge pin located beneath the surface of the upper deck of the frame, but without occupying any space within the pit access opening itself. The pit lid hinge mechanism of the invention provides full clearance to personnel entering or reaching into the access opening within the frame. There is no spring mechanism obstructing entry into or egress from the pit enclosure, and there is no mechanism that occupies any space within the pit enclosure itself.
In one broad aspect the invention may be considered to be an aircraft pit lid assembly comprising a frame with a flat upper deck and defining a hinge pocket recessed beneath the deck, a lid having a flat upper surface with a hinge leaf projecting laterally outwardly from the lid, and a horizontally disposed hinge pin inserted transversely through the hinge leaf and which extends into upright pocket side walls in the recessed pocket in the frame. The horizontal hinge pin thereby form a horizontal axis of lid rotation relative to the frame that lies below the surface of the deck.
The frame is adapted for installation into a surface across which aircraft travel. The frame defines a frame access opening therethrough entirely within its structure. The access opening is surrounded by the flat, horizontal deck. A recessed bearing ledge beneath the deck encompasses the access opening. The hinge pocket that is recessed beneath the deck lies adjacent the access opening and has opposing, mutually upright pocket side walls extending downwardly from the deck. A hinge pocket floor is located between the upright pocket side walls and lies beneath the level of the deck. The pit lid itself has a flat upper surface and is formed of a size and shape that fits within the lateral confines of the deck to rest upon the bearing ledge.
The structure of the frame is bounded by a peripheral edge which extends a short distance vertically downwardly from the deck located therewithin. A straight, laterally extending bore is defined into the peripheral edge and into the structure of the frame parallel to and beneath the deck. The straight bore extends transversely across the hinge pocket so as to intersect the upright pocket side walls. A straight, transverse bore is also defined through the hinge leaf itself. The bores in the structure of the frame and through the hinge leaf are in coaxial alignment with each other. The hinge pin is thereby installed by insertion into the bore in the structure of the frame through a bore opening in the peripheral edge of the frame. The bore may extend entirely through the structure of the frame to thereby form a pair of bore openings at transversely separated locations on the peripheral edge of the frame. Alternatively, the bore may terminate within the structure of the frame and thereby form a single bore opening into the peripheral edge.
In most subsurface pit installations, the top opening of the pit is equipped with a pit liner that defines a flat, upper frame seating surface that extends about the periphery of the pit, and an upwardly projecting rim that forms the outer boundary of the seat for the pit lid frame. The frame of the pit lid assembly is lowered into position to rest upon the frame seat of the pit liner. The rim thereupon surrounds the peripheral edge of the structure of the frame and confines the pit lid frame therewithin. The rim resides in close proximity to the peripheral edge of the pit lid frame. Normally it resides in contact therewith throughout the entire circumference of the peripheral frame edge.
There is really no laterally acting force of any consequence that would tend to push the hinge pin longitudinally within the straight bore within the structure of the lid frame. Nevertheless, the upwardly projecting and surrounding rim of the pit liner effectively blocks the bore opening or openings in the peripheral edge of the frame, and thereby prevents the hinge pin from shifting in either direction along the longitudinal axis of lid rotation once the lid assembly has been seated in the pit liner.
It is important for the pit lid to have a moisture barrier seal at the access opening. In the absence of such a seal, the pit is likely to fill up with dirt and debris that would wash down into the pit access opening during rainy weather or with melting snow. To preserve the integrity of the seal it is highly desirable for the seal to make contact with the lid frame only at the last instance of closure, so that friction between the seal and the surrounding frame is reduced to a minimum.
This objective can be achieved with the pit lid assembly of the invention by forming the pit lid with a perimeter having a seal mounted thereon. The seal forms an enclosed loop that resides in a horizontal sealing plane that seals the pit access opening throughout its entire circumference when the pit lid rests upon the bearing ledge. The hinge pin and the horizontal bore into the structure of the pit frame in which the hinge pin is located, reside in a horizontal plane that is located between the sealing plane and the deck. By locating the hinge pin and the axis of hinge rotation between the sealing plane and the deck, the seal will leave contact with the frame with the first movement of lifting the lid from a closed position. There is therefore very little friction between the seal and the frame as the pit lid is opened and closed. Nevertheless, since the seal does establish contact with the frame at the final instant of closure, the necessary moisture sealing of the access opening is achieved.
Preferably the hinge pocket has an inclined end wall remote from the access opening. The hinge pocket end wall extends between the pocket side walls and is inclined at an obtuse angle, preferably about one hundred twenty degrees, relative to the deck of the pit lit assembly frame. The hinge leaf has a flat upper surface the meets the hinge pocket end wall in surface-to-surface contact when the pit lid is rotated upwardly about the axis of lid rotation to a maximum extent away from the access opening. This construction has several advantages.
The pit lid hinge leaf must have a thickness less than the thickness of the pit lid itself. By making the hinge leaf with a flat upper surface and by locating the hinge pin such that the flat upper surface of the hinge leaf meets the hinge pocket end wall in surface-to-surface contact throughout, a line of stress across the neck of the hinge leaf is avoided. Such a line of stress could result in a fracture of the hinge leaf with repeated use over time, breaking it at its junction with the pit lid. The transition between the hinge leaf and the pit lid is preferably curved so as to provide further strength and avoid a potential fracture line across the hinge leaf.
Another advantage of constructing the hinge leaf and the hinge pocket with flat surfaces that meet in face-to-face contact is that when the pit lid is opened, the flat upper surface of the hinge leaf approaches the hinge pocket end wall in such a manner as to squeeze out debris that may have collected in the hinge pocket between the inclined end wall and the hinge leaf. At airports there is a very significant amount of airport dirt formed of rubber, weeds, and jet fuel. This material accumulates in virtually any recessed surface at the airport, and tends to collect in crevices and cracks. Consequently, there is a considerable likelihood that airport dirt will collect in the hinge pocket at the hinge axis where the hinge leaf is connected by the hinge pin to the pit lid frame.
Preferably the surface of the hinge leaf is flat and meets the end wall surface of the hinge pocket in face-to-face contact throughout as the pit lid is opened to a maximum position at an obtuse angle relative to the plane of the deck of the frame. By constructing the hinge assembly so that the upper surface of the hinge leaf meets the end wall of the leaf pocket in a surface-to-surface contact, a self-cleaning hinge joint is created. That is, as the hinge leaf opens and the angle between the approaching upper surface of the hinge leaf on the stationary end wall of the hinge pocket grows smaller, the airport dirt is squeezed out of the diminishing space between the hinge leaf and the pocket end wall. Since many aircraft service pit lid assemblies remain closed and are not accessed for long periods of time, this self-cleaning feature is important, since it prevents the hinge joint from becoming jammed after a prolonged period of nonuse.
The hinge assembly of the invention is very advantageous because it does not occupy any space within the enclosure of the pit. Rather, the hinge mechanism is set into the structure of the frame at the hinge pocket defined therein.